Leaching assessment

Fait G, Ferrari F, Balderacchi M et al (2008) Herbicide and nitrates groundwater leaching assessment. La Goliardica Pavese, Piacenza... 

Soil core data are available for only six of the pesticides discussed in this paper. The six pesticides are aldlcarb atrazlne 1,2-dibromo-3-chloropropane (DBCP) 1,2-dlchloropro-pane (DCP) 1,2-dlbromoethane (EDB) and slmazlne. Cores were always sampled at depths greater than one meter and the soil was characterized physically and chemically. The importance of soil core sampling in pesticide leaching assessments is presented in the Discussion section. 

For the assessment, an average of 24 cm/yr of irrigation was applied during June, July, August, and September, at daily rates of 2.5 cm only when rain had not fallen for at least four days. A surrmary of the leaching assessment scenarios are given on Table VI. 

Table VII. Summary of water balance for leaching assessment simulations (all units in cm/yr average).

Table VIII summarizes aldicart) fate and transport results for the 5-year leaching assessments, including the percent of applied aldicart) predicted to leach below 2 meters and soluble concentrations at 2 meters. These soluble concentrations are described as "plume11 and "average". The plume concentration has been arbitrarily defined as an average of a continuous six-month period of high aldicarb concentration at the 2-meter depth, which occurs before the next application of aldicarb. This recognizes that aldicarb does, in fact, move with a plume and the plume will pass the 2-meter mark for approximately a 6 month period. For a May application, the plume usually reached the 2-meter mark by June.

Table VIII. Leaching assessment results for aldicarb including percent of applied to leach below two meters, average annual soil water concentrations at two meters, and plume concentrations at two meters. ...

The tests of a capsule design may be performed with simulated radioactive material. The term simulated means a facsimile of a radioactive sealed source, the capsule of which has the same construction and is made with exactly the same materials as those of the sealed sonrce that it represents, but contains, in place of the radioactive material, a substance with mechanical, physical and chemical properties as close as possible to those of the radioactive material and containing radioactive material of tracer quantities only. The tracer should be in a form soluble in a solvent which does not attack the capsule. One procedure described in ISO 2919 [1] utilizes either 2 MBq of Sr-90 and Y-90 as soluble salt, or 1 MBq of Co-60 as soluble salt. When possible, shorter lived nnclides should be used. However, if leaching assessment techniqnes are used, care needs to be taken when interpreting the results. The effects of scaling will have to be introduced, the importance of which will depend upon the maximum activity to be contained within the capsule and also the physical form of the intended capsule contents, particularly the solubility of the intended capsule contents as compared with the tracer radionuclide. These problems can be avoided if volumetric leakage tests are used (see paras 603.3 and 603.4). Typically, tests for special form radioactive material are performed on full scale sealed sources or indispersible soUd material because these are not expensive and the results of the tests are easy to interpret. 

For specimens which comprise or simulate radioactive material enclosed in a sealed capsule, either a leaching assessment as required in para. 711(a) or one of the volumetric leakage assessment methods as specified in para. 711(b) should be applied. The leaching assessment is similar to the method applied to indispersible solid material (see para. 710), except that the specimen is not initially immersed in water for seven days. The other steps, however, remain the same. 

Specimens that comprise or simulate special form radioactive material shall be subjected to the impact test, the percussion test, the bending test and the heat test specified in paras 705-709. A different specimen may be used for each of the tests. Following each test, a leaching assessment or volumetric leakage test shall be performed on the specimen by a method no less sensitive than the methods given in para. 710 for indispersible solid material or in para. 711 for encapsulated material. 

For specimens which comprise or simulate indispersible solid material, a leaching assessment shall be performed as follows ... 

Lincoln JD, Ogunseitan OA, Shapiro AA et al (2007) Leaching assessments of hazardous materials in cellular telephones. Environ Sci Technol 41(7) 2572-2578 Makris KC, Andra SS, Herrick L et al (2013) Association of drinking-water source and use characteristics with urinary antimony concentrations. J Expo Sci Environ Epidemiol 23(2) 120-127... 

Diffusion and Mass Transfer During Leaching. Rates of extraction from individual particles are difficult to assess because it is impossible to define the shapes of the pores or channels through which mass transfer (qv) has to take place. However, the nature of the diffusional process in a porous soHd could be illustrated by considering the diffusion of solute through a pore. This is described mathematically by the diffusion equation, the solutions of which indicate that the concentration in the pore would be expected to decrease according to an exponential decay function. 

Performance assessments are predictions of radioactivity releases, the rate of transfer of contaminants through various media, and the potential for hazard to the pubHc. These are based on a combination of experimental data obtained in the process called site characterization and detaded computations about radionuchdes and their effects. The progressive attack on the metal or ceramic waste container, the diffusion of water into the waste form, the leaching of the radioactive compounds, diffusion out, and washing away of radionuchdes are all considered. 

Periodic samples should he taken to assess the extent of completion of the hioconversion process. Core samples should he taken annually to monitor the movement of leached wastes in the underlying strata. 

The behavior of elements (toxicity, bioavailability, and distribution) in the environment depends strongly on their chemical forms and type of binding and cannot be reliably predicted on the basis of the total concentration. In order to assess the mobility and reactivity of heavy metal (HM) species in solid samples (soils and sediments), batch sequential extraction procedures are used. HM are fractionated into operationally defined forms under the action of selective leaching reagents. 

The proposed method can be applied to the speciation analysis of environmental solids for risk assessment of their contaminants as well as to design of effective leaching schemes. 

The ability of polyvalent cations leached from the glass to suppress the free-fluoride ion concentration in basalt ground water is difficult to assess. Fluoride definitely enhances leaching and is the primary cause of the high concentrations of dissolved plutonium in the basalt ground-water leachate. Once the plutonium is dissolved, however, it is not possible to determine what fraction is stabilized by fluoride as opposed to other species leached from the glass. 

For the various AB cements used in clinical dentistry, erosion and/or leaching of components have been considered important in assessing durability (Wilson McLean, 1988). In fact, the two aspects are not... 

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